The present invention relates to a silver halide emulsion which is low in generation of fog notwithstanding high sensitivity, excellent in a reciprocity law characteristic at high intensity illuminance, and low in fluctuations in sensitivity and gradation due to the time variation after exposure until processing, and also relates to a producing method of the same and a silver halide color photographic material containing the same.
In the field of color photographic paper, demands for performances such as higher sensitization, stabilization of processing, the improvement of image quality and the improvement of development processing speed have been remarkably increased in recent years. In higher sensitization of a silver chloride emulsion, the incorporation of a bromide ion into the emulsion grain has been primarily discussed. For example, a method of incorporating a bromide ion into the surface of a grain is disclosed in EP 0295439, a method of incorporating an epitaxially formed local phase having a bromide concentration of at least 20 mol % into the grain surface is disclosed in U.S. Pat. No. 5,252,454, and a method of blending a fine grain emulsion with a high silver chloride host grain emulsion having larger grain size and performing Ostwald ripening to thereby form a bromide rich phase on the surface of a grain is disclosed in U.S. Pat. No. 5,252,456. On the other hand, sensitivity is also increased by incorporating an iodide ion into a silver chloride emulsion grain. However, the examples of using iodide ions for the purpose of higher sensitization are not so many hitherto and, as represented by the above-cited patents, iodide ion is in general permitted only in low concentration or avoided.
Some examples of achieving higher sensitization by the incorporation of an iodide ion in a high silver chloride emulsion are shown below. Techniques of forming a high silver chloride {100} tabular grain and then incorporating an iodide ion into the grain in the state of a band are disclosed in U.S. Pat. Nos. 5,264,337, 5,292,632 and 5,314,798. An example of epitaxially adhering a bromide ion and a low iodide content ion in combination on the corners of a tabular grain is disclosed in U.S. Pat. No. 5,275,930. JP-A-8-220681 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), JP-A-8-234340, JP-A-8-220684, JP-A-8-240879 and JP-A-8-234345 disclose in common various designs of the incorporation of an iodide ion into a high silver chloride host grain and these patents contrive to have the largest iodide ion concentration in the sub-surface of an emulsion grain and form intentionally a high silver chloride layer not containing an iodide on the layer containing an iodide.
When an iodide ion is subjected to mixed-crystallization to a silver chloride, silver ions between lattices of the inside of a grain conspicuously increase. Therefore, the improvement of sensitization by an iodide ion seems as the acceleration of formation of a light-sensitive speck due to the increment of silver ions between lattices. Since there is not the layer containing an iodide on the surface or an iodide is limited to the corners in the above-exemplified patents, the maximum of the effect of higher sensitization cannot be brought out. Contrary to this, when an iodide ion is contained only on the outermost surface of a grain, the iodide ion adsorbed onto the outermost surface of the grain after grain formation is unstably incorporated into a silver chloride layer by the process after that, e.g., by chemical sensitization, as a result, fog is liable to occur hence unsuitable for the achievement of higher sensitization.
Accordingly, the objects of the present invention is to provide a silver halide emulsion which is low in generation of fog notwithstanding high sensitivity, excellent in a reciprocity law characteristic at high intensity illuminance, and low in fluctuations in sensitivity and gradation due to the time variation after exposure until processing, and to provide a producing method of the same and a silver halide color photographic material containing the same.
As a result of eager investigation by the present inventors, the above objects have been achieved by the following means (1) to (11).
(1) A silver halide photographic emulsion comprising silver chloroiodide grains or silver chloroiodobromide grains having 90 mol % or more of a silver chloride content, wherein the silver chloroiodide grains or silver chloroiodobromide grains have a layer having a silver iodide content of decreasing in the depth direction from the grain surface.
(2) The silver halide photographic emulsion as described in the above item (1), wherein the silver halide photographic emulsion is produced by a method of finishing the introduction of the iodide ion before 98% of the volume of the grains are formed.
(3) The silver halide photographic emulsion as described in the above item (1) or (2), wherein the introduction of the iodide ion is carried out by using silver halide fine grains containing silver iodide.
(4) A silver halide photographic emulsion comprising silver chloroiodide grains or silver chloroiodobromide grains, having 90 mol % or more of a silver chloride content, wherein the introduction of the iodide ion is carried out by using silver halide fine grains containing silver iodide which are formed by providing and mixing an aqueous solution of a water-soluble silver salt and an aqueous solution of a water-soluble halide compound containing the iodide ion in a mixing vessel which is provided separately from a reaction vessel in which a nucleation and/or grain growth of the silver halide grain is carried out.
(5) The silver halide photographic emulsion as described in the above item (3) or (4), wherein said silver halide fine grains have a grain size of 0.06 xcexcm or less.
(6) The silver halide photographic emulsion as described in any of the above items (1) to (5), wherein the main planes of the silver chloroiodide grains or silver chloroiodobromide grains comprise {100} faces.
(7) The silver halide photographic emulsion as described in any of the above items (1) to (6), wherein the silver chloroiodide grains or silver chloroiodobromide grains contain one or more transition metal complexes.
(8) The silver halide photographic emulsion in any of the above items (1) to (7), wherein the content of the iodide ion is 0.1 mol % or more of the total silver amount of the entire emulsion grains.
(9) The silver halide photographic emulsion in any of the above items (1) to (8), wherein the content of the iodide ion is 0.06 mol % or more of the total silver amount of the entire emulsion grains and the silver halide emulsion is spectrally sensitized with a trimethine cyanine dye.
(10) The silver halide photographic emulsion as described in the above item (7) or (9), wherein the content of the iodide ion is 0.06 mol % or more of the total silver amount of the entire emulsion grains and the central metal of at least one kind of the transition metal complex is ruthenium or osmium.
(11) A silver halide color photographic material comprising a support having provided thereon at least one blue-sensitive silver halide emulsion layer, at least one green-sensitive silver halide emulsion layer and at least one red-sensitive silver halide emulsion layer, wherein at least one of the blue-sensitive silver halide emulsion layer, thee green-sensitive silver halide emulsion layer and the red-sensitive silver halide emulsion layer contains the silver halide emulsion described in any of the above items 1 to 10.